Controller for internal combustion engine and method for variable valve timing control for the same

ABSTRACT

A controller is provided to an engine including a variable valve timing unit for manipulating a valve timing of an intake valve of the engine. The controller includes an idle-continuation determining unit for determining whether an idling operation of the engine is in a continued state. The controller further includes a torque reserve control unit for executing a torque reserve control to advance the valve timing and increase an intake air quantity of the engine within a combustion limit of the engine when the idle-continuation determining unit determines that the idling operation is in the continued state. The controller further includes a torque correction unit for executing a torque correction control to retard the valve timing in the torque reserve control in at least one of conditions where: an auxiliary device exerts a load; the load is increased; and a vehicle starts moving.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by reference Japanese Patent Application No. 2006-329062 filed on Dec. 6, 2006.

FIELD OF THE INVENTION

The present invention relates to a controller for an internal combustion engine provided with a variable valve timing unit for varying opening and closing timings of an intake valve of the internal combustion engine The present invention further relates to a method for a variable valve timing control for the internal combustion engine.

BACKGROUND OF THE INVENTION

For example, when an auxiliary device applies a load to an internal combustion engine during an idling operation of the engine, or when the load is increased during the idling operation, an increase in a torque of the engine is demanded. Alternatively, when a vehicle starts during the idling operation, an increase in the torque of the engine is also demanded. The auxiliary device may be an air conditioner, a power steering, and the like.

Conventionally, in such a demand in torque, throttle positions of a throttle valve and an idling speed control valve (ISC valve) are corrected to increase an intake air quantity, whereby a torque loss caused by the load of the auxiliary device are compensated for and the torque of the engine can be increased at the start of the vehicle. In this correction of the throttle positions, a torque fluctuation (torque reduction) caused by the load of the auxiliary device and a torque shortage at the start of the vehicle are suppressed so as to reduce a lag in an actual torque relative to a demand torque.

However, an actual change in the in-cylinder charging air delays relative to the manipulation of the throttle valve and the ISC valve. In addition, a response of the torque of the engine caused by the charging air also delays relative to the manipulation. Therefore, only with the manipulation of the positions of the throttle valve and the ISC valve, the actual torque cannot be controlled with good response relative to the fluctuation in the demand torque. Thus, the idling speed cannot be sufficiently maintained.

An in-cylinder charging efficiency can be changed with good response by switching over opening and closing characteristics such as a working angle and a lift of an intake valve and an exhaust valve of an internal combustion engine. Therefore, a torque in a system provided with the variable valve unit can be manipulated with good response by switching over the opening and closing characteristics. U.S. Pat. No. 5,446,359 (JP-A-H8-338273) discloses a variable valve unit that manipulates a valve opening characteristic and a valve closing characteristic by switching cams, which drive an intake valve and an exhaust valve of an internal combustion engine. Specifically, in U.S. Pat. No. 5,446,359, a normal cam is switched to an auxiliary device actuation cam to switch over the valve opening and closing characteristics, when the auxiliary device such as an air conditioner and the like operates during the idling operation. The torque can be increased by switchover of the valve opening and closing characteristics. Thus, a torque loss caused by a load of the auxiliary device can be compensated for with good response to maintain the idling speed.

However, the system provided with the variable valve timing involves a problem. Specifically, when the load caused by the auxiliary device is applied or increased during the idling operation, or when the vehicle is started, torque may not be produced sufficient to compensate for a demand for an increase in torque or to maintain the idling speed, even manipulating opening and closing timings of an intake valve from an advance angle position suited to the idling operation at the normal idling.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, it is an object of the present invention to produce a controller for an internal combustion engine of a vehicle, the controller being adapted to suppressing torque fluctuation to maintain an engine speed. It is another object of the present invention to produce a method for a variable valve timing control for the internal combustion engine.

According to one aspect of the present invention, a controller for an engine of a vehicle, the engine including a variable valve timing unit for manipulating an intake valve timing including opening and closing timings of an intake valve of the engine, the controller comprising an idle-continuation determining unit for determining whether an idling operation of the engine is in a continued state. The controller further comprises a torque reserve control unit for executing a torque reserve control for advancing the intake valve timing and increasing an intake air quantity of the engine within a combustion limit of the engine when the idle-continuation determining unit determines that the idling operation is in the continued state. The controller further comprises a torque correction unit for executing a torque correction control to retard the intake valve timing in the torque reserve control in at least one of conditions where: an auxiliary device of the vehicle exerts a load; the load is increased; and the vehicle starts moving.

According to another aspect of the present invention, a method for a variable valve timing control for an engine of a vehicle, the method comprising determining whether an idling operation of the engine is in a continued state. The method further comprising executing a torque reserve control for advancing an intake valve timing, which includes opening and closing timings of an intake valve of the engine, and increasing an intake air quantity of the engine within a combustion limit of the engine when the idling operation is in the continued state. The method further comprising executing a torque correction control to retard the intake valve timing in the torque reserve control in at least one of conditions where: an auxiliary device of the vehicle exerts a load to the engine; the load is increased; and the vehicle starts moving.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a view showing an outline of a whole engine control system in an embodiment;

FIG. 2 is a view schematically showing a variable valve timing unit and its hydraulic control circuit;

FIG. 3 is a view illustrating a retard angle operation, a holding operation, and an advance angle operation of the variable valve timing unit;

FIG. 4 is a time chart illustrating a determination of an idle-continuation;

FIG. 5 is a time chart illustrating a determination of a starting condition:

FIG. 6 is a time chart illustrating a torque reserve control;

FIG. 7 is a time chart illustrating the torque reserve control;

FIG. 8 is a time chart illustrating a torque correction control;

FIG. 9 is a time chart illustrating the torque correction control;

FIG. 10 is a flowchart illustrating a VVT control routine;

FIG. 11 is a flowchart illustrating a target advance angle calculating routine;

FIG. 12 is a flowchart illustrating an idle-continuation target advance angle calculating routine;

FIG. 13 is a flowchart illustrating the idle-continuation target advance angle calculating routine;

FIG. 14 is a flowchart illustrating a throttle position control routine;

FIG. 15 is a flowchart illustrating a target throttle position calculating routine;

FIG. 16 is a flowchart illustrating an idle-continuation target throttle position calculating routine;

FIG. 17 is a flowchart illustrating the idle-continuation target throttle position calculating routine;

FIG. 18 is a flowchart illustrating an idle-continuation determining routine; and

FIG. 19 is a flowchart illustrating a combustion limit determining routine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Embodiment

First, an outline of a whole engine control system is described with reference to FIG. 1. An air cleaner 53 is provided upstreammost of an intake pipe 52 of an internal combustion engine 51. An air flowmeter 54 is provided downstream of the air cleaner 53 to detect an intake air quantity. A throttle valve 56 and a throttle position sensor 57 are provided downstream of the air flowmeter 54. A motor 55 is provided to control an opening, i.e., position of the throttle valve 56. The throttle position sensor 57 detects the opening (throttle position) of the throttle valve 56.

A surge tank 58 is provided downstream of the throttle valve 56. An intake-pipe pressure sensor 59 is provided to the surge tank 58 to detect pressure in an intake pipe. The surge tank 58 is provided with intake manifolds 60, which lead air into respective cylinders of the engine 51. Fuel injection valves 61 are respectively provided in the vicinity of intake ports of the intake manifolds 60 for respective cylinders of the engine to inject fuel. Ignition plugs 62 are mounted to a cylinder head of the engine 51 to ignite air-fuel mixture in the cylinders by generating spark discharge.

The engine 51 is provided with a vane type variable valve timing unit 11, which varies a valve timing (opening and closing timing) of an intake valve 67. An exhaust pipe 63 of the engine 51 is provided with an exhaust gas sensor 64 such as an air-fuel ratio sensor and an oxygen sensor for detecting an air-fuel ratio of exhaust gas or rich and lean conditions of exhaust gas. A catalyst 65 such as a three-way catalyst is provided downstream of the exhaust gas sensor 64 for purification of exhaust gas.

A cylinder block of the engine 51 is provided with a cooling-water temperature sensor 66 and a crank angle sensor 44. The cooling-water temperature sensor 66 detects temperature of cooling water of the engine 51. The crank angle sensor 44 outputs a pulse signal each time where the engine 51 rotates by a predetermined crank angle. The crank angle and an engine speed are detected on the basis of an output signal from the crank angle sensor 44. Further, an accelerator position corresponding to depression of an accelerator pedal is detected by an accelerator sensor 68.

Outputs of such various sensors are input into an electronic control unit (ECU) 43. The ECU 43 is constructed mainly of a microcomputer to execute various engine control programs stored in a built-in ROM (memory medium) to control fuel injection quantities of the fuel injection valves 61 and ignition timings of the ignition plugs 62 according to an engine operating state.

Subsequently, the construction of the vane type variable valve timing unit 11 is described with reference to FIG. 2. A housing 12 of the vane type variable valve timing unit 11 is screwed and fixed to a sprocket by bolts 13. The sprocket is rotatably supported on an outer periphery of a camshaft (not shown) of the intake valve. In this structure, rotation of a crankshaft of an engine is transmitted to the sprocket and the housing 12 via a timing chain, so that the sprocket and the housing 12 rotate in synchronism with the crankshaft. A vane rotor 14 is received in the housing 12 such that the vane rotor 14 is rotatable relative to the housing 12. The vane rotor 14 is screwed and fixed to an end of the camshaft by a bolt 15.

Multiple vane chambers 16 are formed in the housing 12. The vane chambers 16 respectively receive multiple vanes 17 provided to an outer periphery of the vane rotor 14. The vanes 17 are rotatable in the vane chambers 16 in both advance and retard angle directions. Each of the vane chambers 16 is partitioned into an advance angle chamber 18 and a retard angle chamber 19 by each of the vanes 17.

When hydraulic pressure equal to or greater than a predetermined pressure is exerted to both the advance angle chambers 18 and the retard angle chambers 19, the vanes 17 are held by the hydraulic pressure. In this condition, rotation of the housing 12 caused by rotation of the crankshaft is transmitted to the vane rotor 14 via the hydraulic pressure, and the camshaft is rotationally driven integrally with the vane rotor 14. While the engine operates, a hydraulic control valve 21 controls hydraulic pressure in the advance angle chambers 18 and the retard angle chambers 19 to turn the vane rotor 14 relative to the housing 12, thereby controlling a displacement angle (camshaft phase) of the camshaft relative to the crankshaft to vary a valve timing of the intake valve 67.

One of the vanes 17 has both sides provided with stopper portions 22, 23 for restriction of a rotative range, in which the vane rotor 14 turns relative to the housing 12. Specifically, the stopper portions 22, 23 restricts an aftermost retard angle position and a foremost advance angle position of a displacement angle of the camshaft. One of the vanes 17 is provided with a lock pin 24, which locks the displacement angle of the camshaft at a predetermined locked position when the engine stops, or the like. When the lock pin 24 is locked, the lock pin 24 is fitted into a lock hole (not shown) provided to the housing 12 to hold the displacement angle of the camshaft at the predetermined locked position. The locked position is set at a position suited to starting of the vehicle. The locked position is, for example, a substantially intermediate position in a controllable range, in which the displacement angle of the camshaft can be controlled.

Working oil in an oil pan 26 is fed through the hydraulic control valve 21 to a hydraulic control circuit of the variable valve timing unit 11 by an oil pump 27. The hydraulic control circuit is provided with hydraulic pressure feed passages 28, 29. Oil is discharged from an advance angle pressure port of the hydraulic control valve 21, and is fed to the advance angle chambers 18 through the hydraulic pressure feed passages 28. Oil is discharged from a retard angle pressure port of the hydraulic control valve 21, and is fed to the retard angle chambers 19 through the hydraulic pressure feed passages 29.

Check valves 30, 31 are provided for restriction of a counterflow of the working oil from the respective chambers 18, 19. The check valves 30, 31 respectively have the hydraulic pressure feed passages 28 of the advance angle chambers 18 and the hydraulic pressure feed passages 29 of the retard angle chambers 19. According to the embodiment, the check valves 30, 31 are provided to the hydraulic pressure feed passages 28, 29 of the advance angle chamber 18 and the retard angle chamber 19 of only one vane chamber 16. Alternatively, the check valves 30, 31 may be provided to the hydraulic pressure feed passages 28, 29 of the advance angle chambers 18 and the retard angle chambers 19 of two or greater vane chambers 16.

Drain oil passages 32, 33 are respectively provided in parallel with the hydraulic pressure feed passages 28, 29 of the respective chambers 18, 19. The drain oil passages 32, 33 respectively bypass the check valves 30, 31. Drain change-over valves 34, 35 are provided respectively to the drain oil passages 32, 33. Each of the drain change-over valves 34, 35 include a spool valve operated in a valve closing direction by being exerted with hydraulic pressure (pilot pressure) from a hydraulic change-over valve 38. The drain change-over valves 34, 35 are respectively held at valve open positions by springs 41, 42 when not being exerted with the hydraulic pressure. When the drain change-over valves 34, 35 are opened, the drain oil passages 32, 33 are opened, thereby defeat operations of the check valves 30, 31. By contrast, when the drain change-over valves 34, 35 are closed, the drain oil passages 32, 33 are closed, thereby enabling the check valves 30, 31. In this condition, the check valves 30, 31 respectively restrict counterflow of oil from the chambers 18, 19, thereby maintaining hydraulic pressure in the chambers 18, 19.

Since the respective drain changeover valves 34, 35 need not electric wiring, the drain change-over valves 34, 35 are assembled compactly to the vane rotor 14 in the vane type variable valve timing unit 11 together with the check valves 30, 31. Thereby, the drain change-over valves 34, 35 are arranged near the respective chambers 18, 19 to enable opening and closing of the respective drain oil passages 32, 33 near the respective chambers 18, 19 with good response at the time of advance angle and retard angle operations.

The hydraulic control valve 21 includes an advance and retard angle hydraulic control function 37 and the hydraulic change-over valve (drain change-over control function) 38 integrated with each other. The advance and retard angle hydraulic control function 37 includes a spool valve driven by a linear solenoid 36 for control of hydraulic pressure fed to the advance angle chambers 18 and the retard angle chambers 19. The hydraulic change-over valve (drain change-over control function) 38 is provided for change-over of hydraulic pressure for driving the respective drain change-over valves 34, 35. The ECU 43 controls an electric current (control duty) carried to the linear solenoid 36 of the hydraulic control valve 21.

The ECU 43 calculates an actual valve timing (actual displacement angle) of the intake valve 67 on the basis of output signals from the crank angle sensor 44 and a cam angle sensor 45. The ECU 43 further calculates a target valve timing (target displacement angle) of the intake valve 67 on the basis of outputs from various sensors such as the intake-pipe pressure sensor 59 and the cooling-water temperature sensor 66 for detecting an engine operating state. The ECU 43 executes routines for control of a variable valve timing to perform a feedback control of a drive current of the hydraulic control valve 21 of the variable valve timing unit 11 such that the actual valve timing agrees with the target valve timing. Hydraulic pressure in the advance angle chambers 18 and the retard angle chambers 19 is controlled to turn the vane rotor 14 relative to the housing 12, thereby changing the displacement angle of the camshaft such that the actual valve timing agrees with the target valve timing.

When the intake valve 67 is driven to open and close while the engine operates, a torque fluctuation is applied to the camshaft from the intake valve 67 and is transmitted to the vane rotor 14, whereby torque fluctuation in the advance and retard angle directions acts on the vane rotor 14. Therefore, when the torque fluctuation is applied to the vane rotor 14 in the retard angle direction, the working oil in the advance angle chambers 18 is applied with pressure and pushed out from the advance angle chambers 18. When torque fluctuation is applied to the vane rotor 14 in the advance angle direction, the working oil in the retard angle chambers 19 is applied with pressure and pushed out from the retard angle chambers 19. When rotation speed of the oil pump 27 being a hydraulic pressure supply source is low, hydraulic pressure of the oil pump 27 becomes low. In this condition, in a structure where the check valves 30, 31 are not provided, the vane rotor 14 is pushed back to the retard angle direction by the torque fluctuation even when the oil pump 27 feeds the hydraulic pressure to the advance angle chambers 18 to advance the displacement angle of the camshaft. As a result, controlling of the vane rotor 14 at the target displacement angle takes long, and a response of the control becomes low.

In contrast, according to the embodiment, the check valves 30, 31 are respectively provided to the hydraulic pressure feed passages 28 of the advance angle chambers 18 and the hydraulic pressure feed passages 29 of the retard angle chambers 19 for restriction of the counterflow of oil from the respective chambers 18, 19. In addition, the drain oil passages 32, 33, which bypass the check valves 30, 31, are respectively provided in parallel with the hydraulic pressure feed passages 28, 29 of the respective chambers 18, 19. Further, the drain change-over valves 34, 35 are respectively provided to the drain oil passages 32, 33. In this structure, as shown in FIG. 3, hydraulic pressure in the respective chambers 18, 19 is controlled in the following retard angle operation, the holding operation, and the advance angle operation.

(Retard Angle Operation)

In the retard angle operation, the actual valve timing is caused to retard toward the target valve timing on the retard angle side. In this retard angle operation, feeding of hydraulic pressure to the drain change-over valve 34 of the advance angle chamber 18 is stopped to open the drain change-over valve 34 of the advance angle chamber 18, thereby defeating the function of the check valve 30 of the advance angle chamber 18. Further, in this retard angle operation, hydraulic pressure is applied to the drain change-over valve 35 of the retard angle chamber 19 from the hydraulic change-over valve 38 to close the drain change-over valve 35 of the retard angle chamber 19, thereby enabling the function of the check valve 31 of the retard angle chamber 19. In this operation, the check valve 31 restricts counterflow of oil from the retard angle chamber 19, and the hydraulic pressure is efficiently fed to the retard angle chamber 19 to enhance a response in the retard angle operation, regardless of torque the fluctuation of the vane rotor 14 in the advance angle direction even when the hydraulic pressure is low.

(Holding Operation)

In the holding operation, the actual valve timing is held at the target valve timing. In this holding operation, hydraulic pressure is applied to both the drain change-over valves 34, 35 of the advance angle chamber 18 and the retard angle chamber 19 from the hydraulic change-over valve 38 to close both the drain change-over valves 34, 35. In this condition, the functions of both the check valves 30, 31 of the advance angle chamber 18 and the retard angle chamber 19 are enabled. When torque applied from the intake valve 67 to the camshaft fluctuates, torque fluctuating in the retard and advance angle directions is applied to the vane rotor 14. In the state of the holding operation, even when the fluctuating torque is applied to the vane rotor 14, the check valves 30, 31 restrict counterflow of oil from both the advance angle chamber 18 and the retard angle chamber 19 to restrict a decrease in hydraulic pressure holding the vanes 17 from both sides thereof. Thus, the holding stability of the vanes 17 can be enhanced.

(Advance Angle Operation)

In the advance angle operation, the actual valve timing is advanced toward the target valve timing on the advance angle side. In this advance angle operation, hydraulic pressure is applied to the drain change-over valve 34 of the advance angle chamber 18 from the hydraulic change-over valve 38 to close the drain change-over valve 34 of the advance angle chamber 18, thereby enabling the function of the check valve 30 of the advance angle chamber 18. Further, in this advance angle operation, feeding of hydraulic pressure to the drain change-over valve 35 of the retard angle chamber 19 is stopped to open the drain change-over valve 35 of the retard angle chamber 19, thereby defeating the function of the check valve 31 of the retard angle chamber 19. In this operation, the check valve 30 restricts counterflow of oil from the advance angle chamber 18, and the hydraulic pressure is efficiently fed to the advance angle chamber 18 to enhance a response in the advance angle operation, regardless the torque fluctuation of the vane rotor 14 in the retard angle direction even when the hydraulic pressure is low.

When an auxiliary device such as an air conditioner and a power steering are operated in a condition where the engine 51 is in an idling operation or the vehicle starts, torque produced by the engine 51 fluctuates and decreases. As a result, the engine speed may decrease due to the load of the auxiliary device and the starting of the vehicle.

As a countermeasure to the decrease in the engine speed, the ECU 43 executes routines for control of the variable valve timing (VVT) and the throttle position shown in FIGS. 10 to 19. The ECU 43 and the routines for control of the VVT and the throttle position shown in FIGS. 10 to 19 serve as a torque reserve control unit and a torque compensation unit.

As shown in a time chart of FIG. 4, at a time point t1, an actual accelerator position AP is less than an idle threshold ID1. The idle threshold ID1 is in the vicinity of a full-close position, for example. In addition, an actual engine speed NE becomes equal to or less than an idle threshold ID2, and a deviation between the actual engine speed NE and a target idling speed is equal to or less than a predetermined value. In this condition, an idle-continuation counter CIDL begins counting. At a time point t2, the idle-continuation counter CIDL exceeds a predetermined value kIDL. In this condition, the idling operation of the engine 51 is determined to be continued, and an idle-continuation flag XIDL is set to 1. This function serves as an idle-continuation determining unit.

Thereafter, as shown in a time chart of FIG. 5, at a time point t3 or at a time point where an actual engine speed NE exceeds the idle threshold 102, when the actual accelerator position AP exceeds the idle threshold ID1, it is determined that the idling operation terminates and a starting condition of the vehicle comes out. In this condition, the idle-continuation flag XIDL is set to 0, and the idle-continuation counter CIDL is set to 0. The idle-continuation counter CIDL may be subjected to a guard-processing with a predetermined upper limit guard value.

In addition, as shown in time charts of FIGS. 6 and 7, at a time point t4, when the idle-continuation flag XIDL is set to 1 and a predetermined condition for executing a VVT in-idling advance control is met, a torque reserve control is executed. In the torque reserve control, an intake valve timing, which is the valve timing of the intake valve 67, is advanced, and an increase correction of the throttle position is performed to increase the intake air quantity. In this operation a decrease in torque caused by the advance of the intake valve timing cancels an increase in torque caused by an increase in intake air quantity. Therefore, the torque can be maintained substantially constant. In addition, to the canceling of the increase in torque, a retard-angle correction of the intake valve timing is executed to increase the torque sufficiently to compensate for a torque loss caused by the load of the auxiliary device and the like. In this state, the decrease in torque by the advance of the intake valve timing is equivalent to a reserve torque, which can be generated by the retard-angle correction of the intake valve timing. In addition, in the course of the torque reserve control, the ignition timing, an in-cylinder charging efficiency, and the like may be corrected according to the advance angle of the intake valve timing in the same manner as at the time of normal operation. The in-cylinder charging efficiency can be corrected by manipulating the exhaust valve timing, correcting the EGR rate, and the like.

In the torque reserve control, as shown in the time chart of FIG. 6, the advance angle of the intake valve timing and the throttle position are regulated such that an intake pressure PM does not exceed a predetermined pressure kPM. In this operation, the intake pressure PM is regulated below a predetermined pressure kVVTPM to be maintained in a negative pressure state, in which a sufficient brake performance for a brake device can be ensured, in the course of torque reserve control. Here, the intake pressure PM of the engine 51 is used to actuate the brake device.

The predetermined pressure kPM is an upper limit value of the intake pressure PM, which can ensure a sufficient brake performance. The predetermined pressure kPM may be set slightly less than the upper limit value.

Further, as shown in the time chart of FIG. 7, in the torque reserve control, a combustion limit of the engine 51 is determined on the basis of a fluctuation in the engine speed NE. The advance angle of the intake valve timing and the throttle position are limited such that a combustion condition of the engine 51 does not exceed the combustion limit, i.e., within the combustion limit.

In the torque reserve control, the advance angle of the intake valve timing and the increase in intake air quantity may be set such that the actual engine speed NE does not fluctuate a predetermined value or greater beyond a target idling speed. In this operation, it is possible to restrict the actual engine speed NE from fluctuating beyond the target idling speed in the torque reserve control. Thus, the idling speed can be stabilized.

Thereafter, as shown in time charts of FIGS. 8, 9, at a time point t5, the auxiliary device is turned ON to apply the load in the course of the torque reserve control. In this condition, an auxiliary device flag XLOAD is set to 1, and a torque correction control is executed.

In this torque correction control, as shown in the time chart of FIG. 8, in the case where the reserve torque is equal to or greater than an auxiliary device demand torque, the retard-angle correction of the intake valve timing is performed by the retard angle corresponding to the auxiliary device demand torque. The reserve torque is the torque, which can be generated by the retard-angle correction of the intake valve timing. The auxiliary device demand torque is a torque required to compensate for the torque loss caused by the load of the auxiliary device. The retard-angle correction of the intake valve timing is performed with good response, so as to temporarily compensate the torque loss caused by the load of the auxiliary device. Thereby, the idling speed can be maintained with good response by suppressing torque fluctuation caused by the load of the auxiliary device in the idling operation.

At a time point t5, the retard-angle correction of the intake valve timing is performed in order to compensate for the torque loss caused by the load of the auxiliary device. In addition, at the time point t5, an increase correction of the throttle position begins to gradually increase the throttle position to regularly compensate for the torque loss caused by the load of the auxiliary device. At the time point t6, a predetermined time kLOAD has elapsed since the time point t5, in which the retard-angle correction of the intake valve timing is performed and the increase correction of the throttle position begins. At the time point t6, the in-cylinder charging air is determined to be actually increasing, and the torque is determined to be also increasing since the increase correction of the throttle position. Therefore, at the time point t6, the advance-angle correction of the intake valve timing is again performed. In this operation, the torque loss is once caused by the load of the auxiliary device, and the torque loss is compensated for by the increase in torque by performing the retard-angle correction of the intake valve timing. The torque compensated for by the retard-angle correction is further compensated for by the increase correction of the throttle position. At that time, the throttle position or the increase correction of the throttle position is stored immediately before the beginning of the increase correction of the throttle position.

Thereafter, at a time point t7, the auxiliary device is turned OFF, and hence the auxiliary device does not apply the load. At the time point t7, a decrease correction of the throttle position is performed to return the throttle position to the throttle position immediately before the starting of the increase correction of the throttle position, and the auxiliary device flag XLOAD is set to 0.

As shown in the time chart of FIG. 9, at a time point t5, the reserve torque is equal to or less than the auxiliary device demand torque, and the auxiliary device flag XLOAD is set to 1 since the auxiliary device is turned ON. At the time point t5, in this condition, a retard-angle correction of the intake valve timing is performed by a retard angle corresponding to the reserve torque. The reserve torque corresponds to the advance-angle correction in the torque reserve control. At the time point t5, in this condition, the increase correction of the throttle position is further performed by a transient correction opening of the throttle valve 56. The transient correction opening of the throttle valve 56 corresponds to a difference between the auxiliary device demand torque and reserve torque. The difference between the auxiliary device demand torque and the reserve torque is a short relative to the auxiliary device demand torque. Thereby, the torque loss caused by the load of the auxiliary device is temporarily compensated for with good response by the retard-angle correction of the intake valve timing and the increase in torque by the increase correction of the throttle position.

In addition, when the idling operation is terminated and starting of the vehicle is detected in the course of the torque reserve control, the retard-angle correction of the intake valve timing is performed by the retard angle corresponding to the reserve torque. The retard angle corresponds to the advance-angle correction by the torque reserve control. Thus, a torque loss caused by the starting of the vehicle is temporarily compensated for with good response by the increase in torque by the retard-angle correction of the intake valve timing. Thereby, the engine speed NE can be maintained with good response by suppressing torque fluctuation caused by the load of the auxiliary device in the idling operation. Thus, torque fluctuation cause by the starting of the vehicle is suppressed with good response and the engine speed NE can be maintained.

The torque reserve control and the torque correction control are executed by the ECU 43 according to the respective programs shown in FIGS. 10 to 19. The processings in the respective routines shown in FIGS. 10 to 19 is described below.

(VVT Control)

A VVT control routine shown in FIG. 10 is executed at a predetermined interval when the ECU 43 is turned ON. When the routine is started up, an operating state, which includes the engine speed NE, the load, the in-cylinder charging efficiency, the cooling-water temperature, and the like, are detected in STEP 101. Thereafter the procedure proceeds to STEP 102 to determine whether a predetermined condition for executing the VVT control is met on the basis of the detected operating state. Consequently, in the case where it is determined that the predetermined condition for executing the VVT control is not met, the routine is terminated without performing processings subsequent to STEP 103.

In contrast, in the case where it is determined that the predetermined condition for executing the VVT control is met in STEP 102, the procedure proceeds to STEP 103. In STEP 103, an actual advance angle of the intake valve timing is calculated in accordance with a phase difference between an output signal of the crank angle sensor 44 and a subsequently generated output signal of the cam angle sensor 45. The actual advance angle corresponds to a present position relative to a most retard angle position. Subsequently, the procedure proceeds to STEP 104. In STEP 104, a target advance angle calculating routine shown in FIG. 11 is executed to calculate a target advance angle VTT of the intake valve timing on the basis of the present operating state and the like.

Thereafter, the procedure proceeds to STEP 105 to execute a VVT control mode determining routine (not shown) to determine whether the VVT control mode is any one of a feedback control mode, a retention control mode, a cleaning mode, and the like, on the basis of the present operating state and the like.

Thereafter, the procedure proceeds to STEP 106 to calculate an OCV target current according to a present VVT control mode such that the actual advance angle of the intake valve timing agrees with the target advance angle VTT Subsequently, the procedure proceeds to STEP 107 to calculate a control duty for controlling the control current of the hydraulic control valve 21 (OCV) at the OCV target current, and the routine is terminated.

(Target Advance Angle Calculation)

A target advance angle calculating routine shown in FIG. 11 is a sub-routine executed in STEP 104 of the VVT control routine shown in FIG. 10. When the routine is started up, the engine speed NE and a load, which corresponds to the intake air quantity and the intake pressure PM, are first detected in STEP 201. The procedure proceeds to STEP 202, in which a reference target advance angle VTTbs corresponding to the engine speed NE and the load is obtained referring to a data map of the reference target advance angle VTTbs. The data map of the reference target advance angle VTTbs is defined such that the reference target advance angle VTTbs becomes 0 at the time of the idling operation.

Thereafter, the procedure proceeds to STEP 203 to execute an idle-continuation target advance angle calculating routine shown in FIGS. 12 and 13 to calculate an idle-continuation target advance angle VTTid at the time of an idle-continuation, in which the idling continues. The procedure proceeds to STEP 204 to add the idle-continuation target advance angle VTTid at the time of the idle-continuation to the reference target advance angle VTTbs to obtain a final target advance angle VTT

VTT=VTTbs+VTTid

(Idle-Continuation Target Advance Angle Calculation)

An idle-continuation target advance angle calculating routine shown in FIGS. 12 and 13 is a sub-routine executed in STEP 203 of the target advance angle calculating routine shown in FIG. 11. When the routine is started up, an operating state, which includes the engine speed NE, the load, the in-cylinder charging efficiency, the cooling-water temperature, and the like, is first detected in STEP 301. The procedure proceeds to STEP 302 to execute an idle-continuation determining routine shown in FIG. 18 to determine whether the idling operation continues. The idle-continuation flag XIDL is set to 1, which indicates that the idling operation continues, or 0 according to the results of determination.

Thereafter, the procedure proceeds to STEP 303 to determine whether the VVT in-idling advance control executing condition is met, depending upon whether the idle-continuation flag XIDL is set to 1 and a normal idling speed control (ISC) executing condition is met.

In the case where it is determined in STEP 303 that the VVT in-idling advance control executing condition is met, the procedure proceeds to STEP 304 to determine whether the auxiliary device is turned ON to apply the load. In the case where it is determined in STEP 304 that the auxiliary device is turned OFF and does not apply the load, the procedure proceeds to STEP 313 to maintain or reset the auxiliary device flag XLOAD to 0 and reset a retard angle shortage ΔVTload to 0.

Thereafter, the procedure proceeds to STEP 314 in FIG. 13 to determine whether the intake pressure PM is less than a predetermined pressure kPM. The predetermined pressure kPM is set to an upper limit value of the intake pressure, which can ensure a sufficient brake negative pressure, or a value slightly less than the upper limit value.

In the case where it is determined in STEP 314 that the intake pressure PM is less than the predetermined pressure kPM, it is determined that a sufficient brake negative pressure can be ensured. In this condition, the procedure proceeds to STEP 315 to perform the increase correction of the idle-continuation target advance angle VTTid by a predetermined value ΔVT1.

VTTid=VTTid+ΔVT1

Thereafter, the procedure proceeds to STEP 316 to execute a combustion limit determining routine shown in FIG. 19 to determine whether a combustion limit is reached on the basis of fluctuation in the engine speed NE. A combustion limit flag XBRNLMT is set to 1, which indicates the combustion limit, or 0 according to the results of the determination.

Thereafter, the procedure proceeds to STEP 317 to determine whether the combustion limit flag XBRNLMT is set to 1. In the case where it is determined that the combustion limit flag XBRNLMT is 0, the idle-continuation target advance angle VTTid is gradually increased by repeating the increase correction of the idle-continuation target advance angle VTTid by the predetermined value ΔVT1. The idle-continuation target advance angle VTTid is gradually increased until it is determined in STEP 314 that the intake pressure PM is equal to or greater than the predetermined pressure kPM, or it is determined in STEP 317 that the combustion limit flag XBRNLMT is set to 1. Thereby, the intake valve timing is gradually advanced when the idle-continuation is determined.

Thereafter, when it is determined in STEP 314 that the intake pressure PM is equal to or greater than the predetermined pressure kPM, the procedure proceeds to STEP 318. In STEP 318, the advance angle of the intake valve timing is limited by performing a decrease correction of the idle-continuation target advance angle VTTid by the predetermined value ΔVT2 to limit the idle-continuation target advance angle VTTid such that the intake pressure PM does not increase beyond the predetermined pressure kPM.

When it is determined in STEP 317 that the combustion limit flag XBRNLMT is set to 1, the procedure proceeds to STEP 318. In STEP 318, the advance angle of the intake valve timing is limited by performing the decrease correction of the idle-continuation target advance angle VTTid by the predetermined value VT2 to regulate the idle-continuation target advance angle VTTid, such that the idle-continuation target advance angle VTTid does not exceed the combustion limit.

After performing the increase correction of the idle-continuation target advance angle VTTid to advance the intake valve timing, when it is determined in STEP 304 shown in FIG. 12 that the auxiliary device is turned ON, the procedure proceeds to STEP 305. In STEP 305, when it is determined that the auxiliary device has just been turned to ON from the OFF state, the procedure proceeds to STEP 306. In STEP 306, an auxiliary device demand retard angle VTload is calculated to conform to the operating state of the auxiliary device and the like with reference to a data map, for example. The data map may be created for each auxiliary device. The auxiliary device demand retard angle VTload is a retard angle of the intake valve timing, which produces the auxiliary device demand torque, which is a torque required to compensate for the torque loss caused by the load of the auxiliary device.

Thereafter, the procedure proceeds to STEP 307 to determine whether the present idle-continuation target advance angle VTTid is equal to or greater than the auxiliary device demand retard angle VTload. That is, in step 307, it is determined whether the reserve torque is equal to or greater than the auxiliary device demand torque. In the case where it is determined in STEP 307 that the idle-continuation target advance angle VTTid is equal to or greater than the auxiliary device demand retard angle VTload, that is, the reserve torque is equal to or greater than the auxiliary device demand torque, the procedure proceeds to STEP 308. In STEP 308, the decrease correction of the idle-continuation target advance angle VTTid is performed by the auxiliary device demand retard angle VTload, and the auxiliary device flag XLOAD is set to 1.

VTTid=VTTid−VTload

XLOAD=1

Thereby, when it is determined that the auxiliary device is turned ON, the retard-angle correction of the intake valve timing is performed by the auxiliary device demand retard angle VTload corresponding to the auxiliary device demand torque. Thus, the torque loss caused by the load of the auxiliary device is temporarily compensated for with good response by the increase in torque by the retard-angle correction of the intake valve timing.

By contrast, in the case where it is determined in STEP 307 that the idle-continuation target advance angle VTTid is less than the auxiliary device demand retard angle VTload, that is, the reserve torque is less than the auxiliary device demand torque, the auxiliary device demand retard angle VTload cannot be ensured even by performing the decrease correction of the idle-continuation target advance angle VTTid to 0. In this condition, the procedure proceeds to STEP 309. In STEP 309, the idle-continuation target advance angle VTTid is subtracted from the auxiliary device demand retard angle VTload to obtain the retard angle shortage ΔVTload for the auxiliary device demand retard angle VTload. The decrease correction of the idle-continuation target advance angle VTTid to 0 is performed, and the auxiliary device flag XLOAD is set to 1.

ΔVTload=VTload−VTTid

VTTid=0

XLOAD=1

Thereby, when it is determined that the auxiliary device is turned ON, the retard-angle correction of the intake valve timing is performed by the retard angle, which is the idle-continuation target advance angle VTTid corresponding to the reserve torque.

In this manner, after the decrease correction of the idle-continuation target advance angle VTTid is performed to retard the intake valve timing, the procedure proceeds to STEP 310. In STEP 310, a counter CLOAD is set to a predetermined count value kLOAD, and then proceeds to STEP 311 to count down the count value of the counter CLOAD by 1 to count the time lapsed after the auxiliary device is turned ON. Thereafter, in the case where it is determined in STEP 305 that the auxiliary device has not just been turned ON, the procedure jumps over the processings of STEPS 306 to 310 to proceed to STEP 311 to count down the counter CLOAD 1 by 1. At this time, the counter CLOAD may be subjected to a guard processing at a lower limit guard value such as 0.

Thereafter, the procedure proceeds to STEP 312 shown in FIG. 13 to determine whether the counter CLOAD is equal to or less than 0. In the case where it is determined that the counter CLOAD is greater than 0, the routine is terminated without performing the processings subsequent to STEP 314. Thereby, another of the advance-angle correction of the intake valve timing is inhibited until beginning of an increase in the torque by increase in the in in-cylinder charging air by the increase correction of the throttle position.

When it is determined in STEP 312 that the counter CLOAD is equal to or less than 0, that is, at the time point when the predetermined time kLOAD lapses, the increase correction of the throttle position leads to an actual increase in the in-cylinder charging air to increase the torque. In this condition, another of the advance-angle correction of the intake valve timing is performed by executing processings of STEP 314 to STEP 318. Thus, the intake pressure PM does not increase beyond the predetermined pressure kPM, and the combustion limit is not exceeded.

In the case where it is determined in STEP 303 shown in FIG. 12 that the VVT in-idling advance control executing condition is not met, it is determined that the idling operation terminates and the vehicle is started, and the procedure proceeds to STEP 319. In STEP 319, the idle-continuation target advance angle VTTid is set to 0, the auxiliary device flag XLOAD is set to 0, and the retard angle shortage ΔVTload is reset to 0. Thereby, the retard-angle correction of the intake valve timing is performed by the retard angle, which is the idle-continuation target advance angle VTTid corresponding to the reserve torque, and the torque loss caused by the starting of the vehicle is temporarily compensated for with good response by the increase in torque by the retard-angle correction of the intake valve timing.

(Throttle Position Control)

The throttle position control routine shown in FIG. 14 is executed at a predetermined interval when the ECU 43 is turned ON. When the routine is started up, an operating state is detected in STEP 401, and then the procedure proceeds to STEP 402 to determine whether a predetermined throttle control executing condition is met, on the basis of the detected operating state. In this condition, the operating state includes the accelerator position, the engine speed NE, an abnormal flag, and the like. Consequently in the case where it is determined that the throttle control executing condition is not met, the routine is terminated without performing the processings subsequent to STEP 403.

In contrast, in the case where it is determined that the throttle control executing condition is met in STEP 402, the procedure proceeds to STEP 403. In STEP 403, the actual throttle position is detected on the basis of the output signal from the throttle position sensor 57. In STEP 404, a target throttle position calculating routine shown in FIG. 15 is executed to calculate a target throttle position TA on the basis of a present operating state and the like.

In STEP 405, a throttle position control mode determining routine (not shown) is executed to determine whether a throttle position control mode is any one of a normal control mode, a limp home control mode, and the like, on the basis of the present operating state and the like. In STEP 406, the control duty of the motor 55 of the throttle valve 56 is calculated according to a present throttle position control mode such that the actual throttle position agrees with the target throttle position TA. Thus, the routine is terminated.

(Target Throttle Position Calculation)

A target throttle position calculating routine shown in FIG. 15 is a sub-routine executed in STEP 404 of the throttle position control routine shown in FIG. 14. When the routine is started up, an accelerator sensor detection value APmad based on an output signal from the accelerator sensor 68 is obtained in STEP 501. In STEP 502, an accelerator full-close position learning routine (not shown) is executed to learn an accelerator full-close position AP0.

Thereafter, the procedure proceeds to STEP 503 to correct the accelerator sensor detection value APmad by using the accelerator full-close position AP0 as learnt to obtain an actual accelerator position AP.

AP=APmad−AP0

Thereafter, the procedure proceeds to STEP 504 to execute an accelerator demand throttle position calculating routine (not shown) to calculate an accelerator demand throttle position TAap conformed to the actual accelerator position AP and the like.

Thereafter, the procedure proceeds to STEP 505 to execute an ISC demand air calculating routine (not shown) to calculate an ISC demand air quantity Qisc on the basis of the target idling speed and the like. The procedure proceeds to STEP 506 to execute an ISC demand throttle position calculating routine (not shown) to calculate an ISC demand throttle position TAisc conformed to the ISC demand air quantity Qisc, and the like.

Thereafter, the procedure proceeds to STEP 507 to execute an idle-continuation target throttle position calculating routine shown in FIGS. 16 and 17 to calculate the idle-continuation target throttle position TAvvt at the time of the idle-continuation.

Thereafter, the procedure proceeds to STEP 508 to obtain a throttle sensor detection value TAmad based on an output signal from the throttle position sensor 57. The procedure proceeds to STEP 509 to execute a throttle full-close position learning routine (not shown) to learn a throttle full-close position TA0.

Thereafter, the procedure proceeds to STEP 510 to calculate a final target throttle position TA by substituting the accelerator demand throttle position TAap, the ISC demand throttle position TAisc, the idle-continuation target throttle position TAvvt, and the throttle full-close position TA0 to the following formula.

TA=TAap+TAisc+TAvvt+TA0

(Idle-Continuation Target Throttle Position Calculation)

An idle-continuation target throttle position calculating routine shown in FIGS. 16 and 17 is a sub-routine executed in STEP 507 of the target throttle position calculating routine shown in FIG. 15. When the routine is started up, an operating state, which includes the engine speed NE, the load, the in-cylinder charging efficiency, the cooling-water temperature, and the like, is first detected in STEP 601. The procedure proceeds to STEP 602 to execute an idle-continuation determining routine shown in FIG. 18 to determine whether the idling operation continues. The idle-continuation flag XIDL is set to 1, which indicates that the idling operation continues, or 0 according to the results of determination.

Thereafter, the procedure proceeds to STEP 603 to determine whether the VVT in-idling advance control executing condition is met, depending upon whether the idle-continuation flag XIDL is set to 1 and a normal idling speed control (ISC) executing condition is met.

In the case where it is determined in STEP 603 that the VVT in-idling advance control executing condition is met, the procedure proceeds to STEP 604 to determine whether the auxiliary device is turned ON to apply the load. In the case where it is determined in STEP 604 that the auxiliary device is turned OFF and the auxiliary device does not apply the load, the procedure proceeds to STEP 612 to perform the decrease correction of an auxiliary device correction opening TAload by a predetermined value ΔTA3.

Thereafter, the procedure proceeds to STEP 613 shown in FIG. 17 to determine whether the intake pressure PM is less than the predetermined pressure kPM. When it is determined that the intake pressure PM is less than the predetermined pressure kPM, the procedure proceeds to STEP 614 to perform the increase correction of a VVT interlocking opening TAvvtb, which is conformed to the advance-angle correction (idle-continuation target advance angle VTTid) of the intake valve timing, by a predetermined value ΔTA4.

TAvvtb=TAvvtb+ΔTA4

Thereafter, the procedure proceeds to STEP 615 to execute a combustion limit determining routine shown in FIG. 19 to determine whether a combustion limit is reached on the basis of fluctuation in the engine speed NE. The combustion limit flag XBRNLMT is set to 1, which indicates the combustion limit, or 0 according to the results of the determination.

Thereafter, the procedure proceeds to STEP 616 to determine whether the combustion limit flag XBRNLMT is set to 1. In the case where it is determined that the combustion limit flag XBRNLMT is set to 0, the VVT interlocking opening TAvvtb is gradually increased by repeating the increase correction of the VVT interlocking opening TAvvtb by the predetermined value ΔTA4, until it is determined in STEP 614 that the intake pressure PM is equal to or greater than the predetermined pressure kPM, or it is determined in STEP 616 that the combustion limit flag XBRNLMT is set to 1. Hereby, the throttle position is gradually increased when the idle-continuation is determined.

Thereafter, when it is determined in STEP 614 that the intake pressure PM is equal to or mort than the predetermined pressure kPM, the procedure proceeds to STEP 617. In STEP 617, the throttle position is limited by performing the decrease correction of the VVT interlocking opening TAvvtb by a predetermined value ΔTA5 to limit the VVT interlocking opening TAvvtb such that the intake pressure PM does not increase beyond the predetermined pressure kPM.

When it is determined in STEP 616 that the combustion limit flag XBRNLMT is set to 1, the procedure proceeds to STEP 617. In STEP 617, the throttle position is limited by performing the decrease correction of the VVT interlocking opening TAvvtb by the predetermined value ΔTA5 to limit the VVT interlocking opening TAvvtb such that the combustion limit is not exceeded.

Thereafter, the procedure proceeds to STEP 618 to add the auxiliary device correction opening TAload to the VVT interlocking opening TAvvtb to obtain the idle-continuation target throttle position TAvvt.

TAvvt=TAvvtb+TAload

In the case where it is determined in STEP 604 shown in FIG. 16 that the auxiliary device is turned ON after performing the increase correction of the idle-continuation target throttle position TAvvt to increase the throttle position, the procedure proceeds to STEP 605. In STEP 605, it is determined whether the retard angle shortage ΔVTload of VVT calculated in STEP 309 shown in FIG. 12 is greater than 0, that is, it is determined whether the idle-continuation target advance angle VTTid is less than the auxiliary device demand retard angle VTload and the reserve torque is equal to or less than the auxiliary device demand torque.

In the case where it is determined in STEP 605 that the retard angle shortage ΔVTload of VVT is greater than 0, the auxiliary device demand retard angle VTload cannot be ensured even when the decrease correction of the idle-continuation target advance angle VTTid is performed to 0. In this condition, the procedure proceeds to STEP 606 to obtain a transient correction opening TAloadc conformed to the retard angle shortage ΔVTload of VVT from a data map or the like. The transient correction opening TAloadc is a throttle position correction magnitude corresponding to torque of the retard angle shortage ΔVTload of VVT and serves to compensate for an intake response delay.

Thereafter, the procedure proceeds to STEP 607 to perform the increase correction of the auxiliary device correction opening TAload by the transient correction opening TAloadc to reset the retard angle shortage ΔVTload of VVT to 0.

TAload=TAload+TAloadc

ΔVTload=0

Thereby, in the case where it is determined that the retard angle shortage ΔVTload of VVT is greater than 0, that is, the reserve torque is less than the auxiliary device demand torque, the retard-angle correction of the intake valve timing by a retard angle (the idle-continuation target advance angle VTTid) corresponding to the reserve torque is performed. In addition, the increase correction of the throttle position is performed by the transient correction opening TAloadc corresponding to the shortage (shortage of VVT in retard angle) in the reserve torque relative to the auxiliary device demand torque. Thus, the torque loss caused by the auxiliary device load is temporarily compensated for with good response by the retard-angle correction of the intake valve timing and the increase in the torque by the increase correction of the throttle position.

Thereafter, the procedure proceeds to STEP 608 to obtain a steady condition auxiliary device demand opening TAloadb conformed to an operating state of the auxiliary device and the like with reference to a data map. The data map may be created for each auxiliary device. The steady condition auxiliary device demand opening TAloadb is the throttle position, which corresponds to the auxiliary device demand torque, which is a torque required to compensate for the torque loss caused by the load of the auxiliary device. The throttle position is to be converged to the steady condition auxiliary device demand opening TAloadb when a steady condition comes out.

Thereafter, the procedure proceeds to STEP 609 to determine whether the auxiliary device correction opening TAload is less than the steady condition auxiliary device demand opening TAloadb. In the case where it is determined that the auxiliary device correction opening TAload is less than the steady condition auxiliary device demand opening TAloadb, the procedure proceeds to STEP 610 to perform the increase correction of the auxiliary device correction opening TAload by a predetermined value ΔTA1. At this time, the auxiliary device correction opening TAload may be subjected to a guard processing at an upper limit guard value. The upper limit guard value may be the steady condition auxiliary device demand opening TAloadb, for example.

TAload=TAload+ATA1

Thereafter, in the case where it is determined in the above-mentioned STEP 609 that the auxiliary device correction opening TAload is equal to or greater than the steady condition auxiliary device demand opening TAloadb, the procedure proceeds to STEP 611 to perform the decrease correction of the auxiliary device correction opening TAload by a predetermined value ΔTA2. At this time, the auxiliary device correction opening TAload may be subjected to a guard processing at a lower limit guard value. The lower limit guard value may be 0, for example.

TAload=TAload−ΔTA2

In this manner the increase correction of the auxiliary device correction opening TAload is performed such that the auxiliary device correction opening TAload agrees substantially with the steady condition auxiliary device demand opening TAloadb. Thereby, the increase correction of the throttle position is performed. In this condition, the torque loss, which is compensated for so far by the increase in torque by the retard-angle correction of the intake valve timing, is compensated by the increase in torque by the increase correction of the throttle position.

Thereafter, when it is determined in STEP 604 that the auxiliary device is turned OFF, and the auxiliary device does not apply the load, the procedure proceeds to STEP 612 to perform the decrease correction of the auxiliary device correction opening TAload by the predetermined value ΔTA3. At this time, the auxiliary device correction opening TAload may be subjected to a guard processing at a lower limit guard value. The lower limit guard value may be 0, for example.

TAload=TAload−ΔTA3

Thereby, the decrease correction of the throttle position is performed to return the throttle position to the throttle position immediately before the increase correction of the throttle position begins.

Thereafter, in the case where it is determined in STEP 603 that the VVT in-idling advance control executing condition is not met, it is determined that the idling operation terminates and the starting condition of the vehicle comes out, and the procedure proceeds to STEP 619. In STEP 619, it is determined whether an accelerator demand throttle position TAap, which is conformed to the actual accelerator position AP and the like, is equal to or greater than the idle-continuation target throttle position TAvvt.

In the case where it is determined in STEP 619 that the accelerator demand throttle position TAap is less than the idle-continuation target throttle position TAvvt, the procedure proceeds to STEP 620 to perform the decrease correction of the idle-continuation target throttle position TAvvt by a predetermined value ΔTA6.

TAvvt=TAvvt−ATA6

Thereafter, when it is determined in STEP 619 that the accelerator demand throttle position TAap is equal to or greater than the idle-continuation target throttle position TAvvt, the procedure proceeds to STEP 621 to reset the idle-continuation target throttle position TAvvt to 0.

After the intake valve timing is caused to retard when the starting condition of the vehicle is detected, the idle-continuation target throttle position TAvvt is set to 0 after the accelerator demand throttle position TAap becomes equal to or greater than the idle-continuation target throttle position TAvvt. Thereafter, the final target throttle position TA is set to the accelerator demand throttle position TAap. Thus, the actual throttle position is smoothly controlled to the accelerator demand throttle position TAap at the starting.

In addition, after the intake valve timing is caused to retard when the starting condition of the vehicle is detected, the actual throttle position may be smoothly controlled to the accelerator demand throttle position TAap by shifting the final target throttle position TA to the accelerator demand throttle position TAap after the accelerator demand throttle position TAap becomes greater than the actual throttle position.

Alternatively, after the intake valve timing is caused to retard when the starting condition of the vehicle is detected, the final target throttle position TA may be gradually shifted to the accelerator demand throttle position TAap by delaying in the control or the like.

(Idle-Continuation Determination)

The idle-continuation determining routine shown in FIG. 18 is a sub-routine executed in STEP 302 shown in FIG. 12 and STEP 602 shown in FIG. 16. When the routine is started up, the actual accelerator position AP is first detected in STEP 701. The procedure proceeds to STEP 702 to determine whether the actual accelerator position AP is equal to or less than the idle threshold ID1, which is, for example, a position in the vicinity of the full-close position.

In the case where it is determined in STEP 702 that the actual accelerator position AP is equal to or less than the idle threshold ID1, the procedure proceeds to STEP 703 to detect the actual engine speed NE. The procedure proceeds to STEP 704 to determine whether the actual engine speed NE is equal to or less than an idle threshold ID2. That is, in STEP 704, it is determined whether a deviation between the actual engine speed NE and the target idling speed is equal to or less than a predetermined value.

When it is determined in STEP 702 that the actual accelerator position AP is equal to or less than the idle threshold ID1, and it is determined in STEP 704 that the actual engine speed NE is equal to or less than the idle threshold ID2, the procedure proceeds to STEP 705 to begin the processing of counting up the idle-continuation counter CIDL 1 by 1.

Thereafter, the procedure proceeds to STEP 706 to determine whether the count value of the idle-continuation counter CIDL is equal to or greater than the predetermined value kIDL. When it is determined that the count value of the idle-continuation counter CIDL is equal to or greater than the predetermined value kIDL, the procedure proceeds to STEP 707, determining that the idling operation of the engine 51 continues, and the idle-continuation flag XIDL is set to 1.

In contrast, in the case where it is determined in STEP 702 that the actual accelerator position AP is greater than the idle threshold ID1, the procedure proceeds to STEP 708. Alternatively, in the case where it is determined in STEP 704 that the actual engine speed NE is greater than the idle threshold ID2, that is, the deviation between the actual engine speed NE and the target idling speed is greater than the predetermined value, the procedure proceeds to STEP 708. In STEP 708, the idle-continuation counter CIDL is reset to 0, and the idle-continuation flag XIDL is maintained or reset to 0.

In the routine shown in FIG. 18, it is determined that the idling operation is in the continued state, when the state, in which the actual accelerator position AP is equal to or less than the idle threshold ID1 and the actual engine speed NE is equal to or less than the idle threshold ID2, that is, the deviation between the actual engine speed NE and the target idling speed is equal to or less than the predetermined value, continues for a predetermined period. The method for determination of the state, in which the idling operation continues, may be appropriately modified. For example, the state, in which the idling operation continues, may be determined when the state, in which the actual accelerator position AP is equal to or less than the idle threshold ID1, continues for a predetermined period. When the accelerator position is returned to the vicinity of the full-close position, the state of idling operation is brought about. Therefore, it possible to accurately determine whether the idling operation continues by monitoring the accelerator position.

The state, in which the idling operation continues, may be determined when a state, in which a deviation between an ISC demand throttle position and the actual throttle position, continues for a predetermined period. Alternatively, the state, in which the idling operation continues, may also be determined when the target throttle position becomes equal to or less than a predetermined value, continues for a predetermined period.

When the target throttle position is set to the ISC demand throttle position and the actual throttle position is controlled at the ISC demand throttle position, the state of idling operation is brought about. Therefore, it possible to accurately determine whether the idling operation continues by evaluating of the deviation between the ISC demand throttle position and the actual throttle position or a target throttle position.

(Combustion Limit Determination)

The combustion limit determining routine shown in FIG. 19 is a sub-routine executed in STEP 316 shown in FIG. 13 and STEP 615 shown in FIG. 17. When the routine is started up, the actual engine speed NE is first detected in STEP 801 and then the procedure proceeds to STEP 802 to calculate an engine speed fluctuation NEfluct. The engine speed fluctuation NEfluct may be calculated by, for example, assuming that a difference between the actual engine speed NE at the last time and the actual engine speed NE at the present time is the engine speed fluctuation NEfluct. Alternatively, the engine speed fluctuation NEfluct may be calculated by assuming that a difference between the maximum value of the actual engine speed NE and the minimum value of the actual engine speed NE in a predetermined period is the engine speed fluctuation NEfluct.

The combustion state of the engine 51 becomes unstable in the vicinity of the combustion limit of the engine 51, and the engine speed fluctuation NEfluct increases. Therefore, it is possible to accurately determine the combustion limit by monitoring the engine speed fluctuation NEfluct.

Thereafter, the procedure proceeds to STEP 803 to determine whether the engine speed fluctuation NEfluct is equal to or greater than the combustion limit determination value kBRN. In the case where it is determined that the engine speed fluctuation NEfluct is equal to or greater than the combustion limit determination value kBRN, the procedure proceeds to STEP 804, determining that the combustion limit of the engine 51 is reached, to set the combustion limit flag XBRNLMT to 1.

In contrast, in the case where it is determined in STEP 803 that the engine speed fluctuation NEfluct is less than the combustion limit determination value kBRN, the procedure proceeds to STEP 805 to maintain or reset the combustion limit flag XBRNLMT at 0.

In the routine shown in FIG. 19, the combustion limit is determined on the basis of the engine speed fluctuation NEfluct. Alternatively, a method for determination of the combustion limit may be appropriately modified, and for example, the combustion limit may be determined on the basis of the air-fuel ratio of the engine 51. The combustion state of the engine 51 becomes unstable in the vicinity of the combustion limit of the engine 51, and the air-fuel ratio of exhaust gas is considerably varied. Therefore, it is possible to accurately determine the combustion limit by, for example, monitoring the variation in air-fuel ratio of exhaust gas.

In the embodiment described above, when it is determined that the idling operation continues, the torque reserve control is executed. In the torque reserve control, the intake valve timing is once advanced, and the increase correction of the throttle position is performed to increase the intake air quantity. Therefore, the torque reserve control enables the retard-angle correction of the intake valve timing to increase the torque enough to compensate for the torque loss caused by the load of the auxiliary device and the like. The torque reserve control performs the retard-angle correction of the intake valve timing, while maintaining the torque substantially constant by decreasing the torque by the advance of the intake valve timing to cancel the increase in torque by the increase in intake air quantity. In this operation, simply advancing of the intake valve timing may lead to deterioration in combustion, nevertheless, the increase in intake air quantity can restrict the deterioration in combustion caused by the advance of the intake valve timing. Thus, a favorable state of combustion can be maintained. Furthermore, a loss in pumping can be decreased by the increase in intake air quantity and/or the increase in intake pressure, so that it is possible to enhance a fuel consumption during the idling operation.

The torque correction control for causing the intake valve timing to retard is executed when the auxiliary device and the like apply the load or the starting condition of the vehicle is detected in the course of the torque reserve control. Therefore, the torque loss caused by the load of the auxiliary device and the starting of the vehicle can be compensated for with good response by increase in the torque by the retard-angle correction of the intake valve timing. Thereby, it is possible to suppress torque fluctuation caused by the load of the auxiliary device at the time of idling operation and starting of the vehicle with good response. Thus, it is possible to effectively restrict a drop in rotating speed at the time of idling operation and at the start.

The torque correction control may be executed when the load of the auxiliary device and the like quickly increases in the course of the torque reserve control.

Here, in a system, in which an intake pressure of the engine 51 is used to actuate a brake device, a sufficient brake negative pressure may not be ensured when the intake pressure excessively increases in torque reserve control.

In this respect, according to the embodiment, the advance angle of the intake valve timing and the throttle position are restricted such that the intake pressure does not exceed a predetermined pressure in the torque reserve control. Therefore, it is possible to restrict the intake pressure to a predetermined pressure or less in the torque reserve control to maintain the intake pressure in a state of negative pressure, such that a sufficient brake performance can be ensured.

In addition, the variable valve timing unit 11 includes the check valves 30, 31, the drain change-over valves 34, 35, and the like being capable of ensuring the responsibility thereof even at low hydraulic pressure. Therefore, the torque reserve control can be executed with good response for advancing the intake valve timing and the torque correction control for causing the intake valve timing to retard, even in the idling operation in the low-speed operation, in which the hydraulic pressure fed from the oil pump 27 is low.

In addition, the variable valve timing unit 11 may be appropriately modified in construction. The variable valve timing unit 11 may be applied to a system mounting thereon various hydraulically driven variable valve timing units such as a vane type variable valve timing unit, in which the check valves 30, 31, the drain change-over valves 34, 35, and the like are omitted. The variable valve timing unit 11 may be applied to a variable valve timing unit other than a vane type variable valve timing unit. For example, the variable valve timing unit 11 may be applied to a helical type variable valve timing unit, and the like.

Further, the invention is not limited to a system mounting thereon a vane type variable valve timing unit but can be variously modified and embodied in application to a system mounting thereon an electrically-driven variable valve timing unit.

The above processings such as calculations and determinations are not limited being executed by the ECU 43. The control unit may have various structures including the ECU 43 shown as an example.

It should be appreciated that while the processes of the embodiments of the present invention have been described herein as including a specific sequence of steps, further alternative embodiments including various other sequences of these steps and/or additional steps not disclosed herein are intended to be within the steps of the present invention.

Various modifications and alternations may be diversely made to the above embodiments without departing from the spirit of the present invention. 

1. A controller for an engine of a vehicle, the engine including a variable valve timing unit for manipulating an intake valve timing including opening and closing timings of an intake valve of the engine, the controller comprising: an idle-continuation determining unit for determining whether an idling operation of the engine is in a continued state; a torque reserve control unit for executing a torque reserve control for advancing the intake valve timing and increasing an intake air quantity of the engine within a combustion limit of the engine when the idle-continuation determining unit determines that the idling operation is in the continued state; and a torque correction unit for executing a torque correction control to retard the intake valve timing in the torque reserve control in at least one of conditions where: an auxiliary device of the vehicle exerts a load; the load is increased; and the vehicle starts moving.
 2. The controller according to claim 1, wherein the torque reserve control unit regulates an advance in the intake valve timing such that a pressure in an intake pipe of the engine is equal to or less than a predetermined pressure in the torque reserve control.
 3. The controller according to claim 1, wherein the torque reserve control unit sets an advance in the intake valve timing and an increase in the intake air quantity such that a variation in an actual speed of the engine is within a predetermined range relative to the target idling speed in the torque reserve control.
 4. The controller according to claim 1, wherein the torque reserve control unit determines the combustion limit on the basis of a fluctuation in a speed of the engine in the torque reserve control.
 5. The controller according to claim 1, wherein the torque reserve control unit determines the combustion limit on the basis of an air-fuel ratio of the engine in the torque reserve control.
 6. The controller according to claim 1, further comprising: a unit for gradually shifting a target throttle position to an accelerator demand throttle position, which is set on the basis of an accelerator position, after the torque correction unit retards the intake valve timing when the vehicle starts moving.
 7. The controller according to claim 1, further comprising: a unit for shifting a target throttle position to an accelerator demand throttle position, which is set on the basis of the accelerator position, since the accelerator demand throttle position becomes greater than a throttle position demanded by the torque reserve control unit, after the torque correction unit retards the intake valve timing when the vehicle starts moving.
 8. The controller according to claim 1, wherein the idle-continuation determining unit determines whether the idling operation is in the continued state on the basis of the accelerator position.
 9. The controller according to claim 8, wherein the idle-continuation determining unit determines that the idling operation is in the continued state in a condition where: the accelerator position is equal to or less than a predetermined threshold; and a deviation between an actual speed of the engine and the target idling speed is equal to or less than a predetermined threshold.
 10. The controller according to claim 1, wherein the idle-continuation determining unit determines whether the idling operation is in the continued state on the basis of a deviation between a throttle position, which produces the target idling speed, and one of an actual throttle position and a target throttle position.
 11. The controller according to claim 1, wherein the variable valve timing unit includes: a housing; a vane that partitions an interior of the housing into an advance chamber and a retard chamber respectively connected with hydraulic passages; a pair of check valves respectively provided to the hydraulic passages for restriction of a counterflow of a working fluid from the advance chamber and the retard chamber, and the hydraulic passages are respectively provided with drain passages being respectively in parallel with the hydraulic passages to respectively bypasses the check valves; and a pair of drain change-over valves respectively provided to the hydraulic passages for communicating and blocking the hydraulic passages.
 12. A method for a variable valve timing control for an engine of a vehicle, the method comprising: determining whether an idling operation of the engine is in a continued state; executing a torque reserve control for advancing an intake valve timing, which includes opening and closing timings of an intake valve of the engine, and increasing an intake air quantity of the engine within a combustion limit of the engine when the idling operation is in the continued state; and executing a torque correction control to retard the intake valve timing in the torque reserve control in at least one of conditions where: an auxiliary device of the vehicle exerts a load to the engine; the load is increased; and the vehicle starts moving. 